The use of various enzymes in animal, e.g., livestock, feed has become almost common practice. These enzymes are usually produced by culturing microorganisms in large scale fermenters operated by industrial enzyme producers. At the end of the fermentation the resulting “broth” is usually subjected to a series of filtration steps to separate the biomass (the microorganisms) from the desired enzyme (in solution). The enzyme solution is either then sold as a liquid (often after addition of various stabilizers) or processed to a dry formulation.
Enzyme liquid and dry formulations are used on a commercial scale by the feed industry. Liquid formulations may be added to the feed after pelleting in order to avoid heat inactivation of the enzyme(s) which would occur during the pelleting process. However the amounts of enzyme in the final feed preparations are usually very small which makes it difficult to achieve a homogenous distribution of the enzyme in the feed, and liquids are notoriously more difficult to mix evenly than dry ingredients. In addition one needs specialised (expensive) equipment to add liquids to the feed after pelleting which is not currently available at most feed mills (due to the extra cost).
Dry formulations of enzyme(s), on the other hand, have the disadvantage of heat-inactivation of the enzymes during pelleting. Preferred manufacturing protocols in the feed industry involve steam pelleting where the feed is subjected to steam injection(s) prior to pelleting. In the subsequent pelleting step the feed is forced through a matrix or die and the resulting strips are cut into suitable pellets of variable length. The moisture content immediately before pelleting is generally between 18% and 19%. During this process temperatures may rise to 60-95° C. The combined effect of high moisture content and high temperature is detrimental to most enzymes.
These disadvantages are also encountered in other types of thermomechanical treatments such as extrusion and expansion.
In order to try and overcome these problems EP-A-0,257,996 (Cultor Ltd.) suggests that the stability of enzymes in feed processing could be increased by the preparation of an enzyme “premix” where an enzyme-containing solution is absorbed onto a grain-based carrier consisting of flour, and the premix is subsequently pelleted and dried. However, these flour-based premixes are not suitable for gentler methods of processing (of the dough-like premix) into granulates, such as low-pressure extrusion or high shear granulation, because of the gluey character of the flour-based premixes.
Various enzyme manufacturers have developed alternative formulation methods to try to improve the stability of dry enzyme products during pelleting and storage.
EP-A-0,569,468 (Novo Nordisk) refers to a formulation consisting of a enzyme-containing “T-granulate” that is coated with a high melting wax or fat alleged to improve resistance to pelleting conditions. The granulate is prepared by mixing a dry inorganic (e.g., sodium sulphate) filler with the enzyme solution in a high shear granulator. EP-A-0,569,468 teaches that any beneficial effect of the coating with respect to pelleting stability is specific for the type of granulate coated, which in this case is based on a sodium sulphate filler. However, the absorption capacity of these (sodium sulphate) fillers is much less than that of carriers such as flour, which is undesirable if one wishes to produce more concentrated enzyme-containing granulates.
In addition, the granulates have a wide particle size distribution which makes it difficult to obtain a homogeneous enzyme concentration throughout. Moreover the bioavailability of the enzyme to the animal is decreased by the wax or fat coating.
WO-A-97/16076 (Novo Nordisk) also refers to the use of waxes and other water-insoluble substances in particulates, but here they are employed as a matrix material.
There is thus a need for stable formulations of enzymes that are based on a carrier that is suitable for granulation methods other than pelleting and that can have a high absorption capacity. Further objects and advantages of the invention will be apparent from the description herein.